Method and apparatus for drying yarn packages in an electrostatic field



2 Sheets-Sheet 1 msm/@vcr A. S. BROWN METHOD AND APPARATUS FOR DRYINGYARN PACKAGES IN AN ELECTROSTATIC FIELD Filed DSC. 30, 1944 WMW Il lOefn 7, 1947.

ff/ew Mipaf/wy Oct 7, 1947.

A. N METHOD AND APPARATUS FOR DRYING YARN PACKAGES IN AN ELEQTROSTATIGFIELD Y Filed D SC. 30, 1944 'Y 2 Sheets-Sheet 2 LFE-#L A IN V EN TOR. AF952 SERoW/v BY UNITED STATES Patented Oct. 7, 1947- METHOD ANDAPPARATUS FOB DRYING PACKAGES IN AN ELECTRDSTATIC Application December30, 1944, Serial No. 570,601

PATENT OFFICE 8 Claims.

'I'his inventionI relates to the drying of yarn packages, and isparticularly described in its application to the removal of water frompackages of viscose -rayon yarn, although it is applicable to theremoval of liquids from other materials also.

In the lmanufacture of rayon yarn by the pot or bobbin systems thedrying of the yarn packages has long been an important problem. Mostmethods of drying such yarn packages use air to carry off the watervapor, usually heating this air to a temperature approximating 150 F.Other methods use vacuum drying in an effort to remove the water.readily at a lower temperature. In general, however, the energyrequired to vaporize water from the yarn package has been supplied bysubstantially thermal conductive means, with the result that the packagedries more quickly in some regions, usually the surfaces, thanin others.Consequently yarns from these different regions of the package differ intextile characteristics.

High frequency electrical helds are capable of heating a packagesubstantially uniformly throughout the mass of such a package whensuitable conditions are imposed. The general idea of heating a yarnpackage by high frequency electric power has been known for a long timeand is, per se, no part of the present invention. However, methods areknown also which involve nonuniform heating of the yarn package. Alsosome methods use costly vacuum systems for boiling lwater at arelatively low temperature.

Pertinen't scientific literature has stated that viscose rayon yarn isweakened by drying at elevated temperatures and at high relativehumidities in the surrounding atmosphere; and it is probable thatcertain prior art methods for drying yarns at lower temperatures werebased upon this belief. I was, therefore, surprised to find that viscoserayon yarn dried at a temperature of about 212 F. in an atmosphere thatis substantially water vapor is at least as strong as yarn dried bycurrent manufacturing methods. Furthermore, I have found that if wateris removed at about 212 F. from a yarn package maintained in anatmosphere that is substantially water vvapor, and the energy needed toremove the water is supplied by high frequency power, a dried packagecharacterized by exceptional uniformity of yarn textile quality isproduced. In addition, I have found that these drying conditions may beaccomplished with relatively simple equipment and in a, surprisinglyeconomical manner.

A principal object of this invention is the .pro-

vision of a, method for drying yarn packages uniformly with respect totextile quality.

A further object of this invention is the provision of an economicalmethod for drying yarn packages with high frequency electric power.

Another object of the present invention is to provide apparatus by whichthe methods hereinabove generally referred to may be carried out in anefficient manner.

A further and more specific object of the present invention is toprovide apparatus for the drying of yarn packages including viscoserayon yarn in a uniform manner, so as to retain the high quality textilecharacteristics of the yarn.

A further object of the present invention is to provide apparatus of asubstantially continuous type by which yarn packages may be dried,utilizing the principles of the present invention as to method and in acommercial manner, that is, for the drying of a large number of yarnpackages.

Other and more detailed objects of the present invention. will becomeapparent from the following specification and appended claims, whentaken in connection with the accompanying drawings. in which:

Figure 1 is an elevation, partly in section, of an apparatus forpracticing this invention;

Fig. 2 is an eevation, partly in section, of a preferred ernho ment ofthis invention;

Fig, 3 is a i f, rincipally in longitudinal section, of apparatus forapplying this invention to the continuous drying of yarn packages; and

Fig. 4 is a 'transverse sectional viev. of the apparatus of Fig. takenon the line llthereof.

Referring now to the accompanying drawings, I have shown in iig. 1, aform of the present invention intended for the drying of one yarnpackage at a time by the use of high frequency electric energy andincluding the establishment of a high frequency field in which the yarnpackage is located, so that heat energy will be substantially uniformlygenerated throughout the yarn package. I have further provided means bywhich the yarn package will be substantially enclosed .by a protectingatmosphere of the vapor of the liquid being evaporated therefrom, which,in the usual case, will be water. 'Ihere is further provided means bywhich the electrodes will be maintained at temperatures at least as highas the boiling temperature of the liquid being evaporated from the yarnpackage, or in the case of water, at least 212 F., the liquid beingevaporated preferably at substantially atmospheric pressure.

In Fig. 1, a yarn package I is supported on a.

metal screen 2 which, in turn. is supported by a framework 3, the screen2 comprising one electrode in a high frequency circuit and beingpreferably grounded as indicated. The screen 2 is preferably maintainedat a temperature of at least about 212 F. by a heating coil 4, which isheated by steam or some other suitable heating fluid. An upper electrode5 in the high frequency circuit is shown spaced above the yarn packageI, although I sometimes prefer to rest this electrode on the yarnpackage. The electrode 5 is preferably maintained at a temperature ofabout 212 F. or somewhat higher by one or more heating means, here shownas lamps 6. The electrode 5 is connected to the high frequency circuitby a lead I which is supported by a high voltage in sulator 8. Theentire cake-electrode assembly is quency electric energy, ortransforming such energy as may be received from a conventional powersupply line into desired high frequency electric energy. This means isnot here illus-- trated ln detail, but is diagrammatically indicated bythe box shown in Fig. 1,- containing the legend High frequency.

In Fig. 2, I have shown another and what I now consider tobe a preferredform ofmy invention as applied to the drying of yarn packages. In thisfigure the yarn package I is shown supported on an annular disk I whichrests on a hollow electrode II, this electrode preferably beingadjustable in a vertical direction by any suitable means (not shown).The disk III is preferably made of some suitable metal, such asstainless steel or aluminum, although it may be constructed of suitablenon-metallic materials, in which case the selected material shouldpreferably havea low electrical loss factor at the high frequencies andhigh temperatures contemplated in this invention. The disk III maysometimes be omitted when drying certain types of yarn packages. Thehollow electrode II is preferably maintained at a temperature-of about212 F. or slightly higher by 'passing through it any suitable heatingmedium. I prefer to operate the electrode II at substantially groundpotential, although this is not necessary if suitable insulatingsupports are provided. When the electrode II is heated by steam suppliedat a pressure somewhat above atmospheric, the upper surface of thiselectrode may be provided with a number of small holes I2 locatedadjacent to the periphery of the disk I0.

. A cloud of steam is thus blown from these holes,

enveloping the yarn package during the drying operation. y

An upper electrode I3 is shown supported from a high voltage insulatorI4 in vertically spaced relationship with the yarn package I. Theelectrode I3 is of hollow construction and is preferably maintained at atemperature of about 212 F. or higher by passing therethrough anysuitable heating medium, which may be supplied through one or moreconnections I5 preferably constructed of suitable glass or rubbertubing. When the heating medium is circulated through the elecbe of somesuitable material, such as glass, having a low electrical loss factor.The means I5 is here shown as a conduit serving to carry any drops ofWater away from the yarn package I, although I have found a simple holeto serve this purpose adequately if the hole is located a short distanceaway from the yarn package.

The observed effects of this invention may be explained by the followingtheoretical considerations, although I do not wish to be limited to anyparticular theory. The heating effect of high frequency power appears tobe closely related to the wetness of the material between theelectrodes. Hence, the uniformity with which ,a package may be thusdried is dependent upon the accuracy with which electrical energy is'caused to evaporate liquid in all regions of the yarn package and atany instant in the drying period. If some other mechanism, such as astream of air oran evacuation system, is simultaneously supplied, thusremoving water vapor differentially to a greater extent from thegenerally outer surfaces of the package, a non-uniformity in the dryingof the several regions of the package is introduced.

`The maintenance of an atmosphere of water vapor substantiallycompletely surrounding thepackage being dried is believed to prevent theevaporation of surface liquid Aat a rate faster than that in theinterior portions of the package. Furthermore, I believe that it isimportant to minimize the loss or gain of heat by thermal conduction andradiation from and to the package, to relate quantitatively thedissipation of electrical energy and the evaporation of liquid. I havefound that a wet ring tends to be left at the region of contact betweenthe yarn package and its support unless the lower electrode is heated toa temperature of about 212 F. or slightly higher, and that such a wetring is removable only with dilculty.

Spacing of the upper electrode I3 from the yarn package I, results indesired structural simplifications. It also appears to be ofconsiderable technical importance in producing uniform heating in thepackage, probably because the spacing contemplated by this invention islarge as compared with the dimensional irregularities usually present insuch yarn packages. I generally use a spacing of about half an inch, al-

though this dimension is not critical. I have also successfully usedspacings of up to about three inches.'

Maintenanceof the upper electrode at a temperature of about 212 orsomewhat higher may be of critical importance in preventing condensationof moisture on the lower side of this electrode. If drops of water fallfrom this electrode onto the yarn package, they often cause arcing,which may shut down the high frequency generator or burn the yarnpackage. Such drops also may carry dirt and result vin the formation ofstains von the yarn package. Furthermore, if a substantial amount ofliquid is returned to the package through such condensation, there mayresult a wet ring about the top of the package. The removal of such aring is not only costly, but also detrimental to the objects of thisinvention as explained above.

The effect of the substantially water vapor atmosphere on the strengthand extensibility characteristics of the yarn is difllcult to explain.It

. may be that the deterioration described in the literature aforesaidwas largely due to oxidation; and that such oxidation is prevented bythe subthe material being ldried.

stantial displacement of airlby water vapor at and adjacent to thesurfaces of the yarn package. It may be simply a reflection of theuniformity with which the yarn package is dried, and the consequentprevention of localized strains.

I have found that yarn from packages dried according to the presentinvention is exceptionally relaxed and uniform. If a measured length ofsuch yarn is wetted and redried under a tension of only a` fewmilligrams per denier, the final length will exceed the original lengthirrespective of the particular region of the package from which the yarnsample may have been selected. Furthermore, the length increasesobserved in such tests will generally vary by only 0.3% to 0.4% yof theoriginal sample lengths. In addition, yarn dried according to thepresent invention has a tenacity and an extensibility at least as highas yarn dried by warm air, `and may even be significantly better.

The present invention also provides relatively simple means for dryingyarn packages with high frequency power, thus making practical the veryfast drying of such packages. For example, the benefits of thisinvention are realized even when the packages are dried at a rate onehundred to two hundred times as fast as obtained in equipment using onlywarm air to dry the yarn.

I have also found that, according to the practice of the presentinvention, drying of the'yarn package may readily be terminated at aselected residual moisture content of, say, for example, about eightpercent, with the result that the subsequent conditioning of thispackage is materially facilitated.

While the present invention has been described in terms of the removalof water from a yarn package, it is contemplated that many of its novelfeatures are applicable to the evaporation of other liquids. In suchother applications it is necessary only that the electrical loss factorof the system be high enough to permit the generation of adequate heat.The system will `operate at substantially the normal boiling point ofthe liquid being evaporated and the vapor of this liquid willsubstantially enclose If the Vapor could be ignited by an accidentalarc, air should be excluded from the drying chamber.

I also contemplate that vapors emitted in the drying chamber of thisinvention may be recovered by any suitable means. If the vapor is steam,it will often be desirable to recover this heat in a suitable condensingsystem, thus obtaining a supply of hot Water. Normally, some air willgain access to the drying chamber and will pass into the recoverysystem, this warm and humid air being of use in air conditioning il the'dryer installation is very large.

Referring now to Figs. 3 and 4 I have shown in somewhat diagrammaticform, an apparatus for the carrying out of the method above outlined ona large number of yarn packages which are moved progressively andpreferably continuously through an elongate drying oven upon an endlessconveyor, so that a large production of dried yarn packages may beobtained. The same principles as to method, and more or less similarapparatus, are employed as have been particularly described in relationto Figs. 1 `and 2. The same advantages are to be gained with theadditional advantage of high production operation such as is necessarywhen operating on a commercial scale.

Referring now more particularly to the drawings, there is shown anelongate drying chamber generally indicated at I1, enclosing a path oftravel for the yarn packages, this chamber having an enlarged centralportion I8 and relatively constricted entrance and exit yarn ports,which may have the form of end portions I9 and 20, respectively, at theends of the path. The yarn packages I, to be dried, are carried throughthe chamber by an endless conveyor generally indicated at 2|, which isshown as being made up of a plurality of panels 22, preferably ofmetallic construction, so that this conveyor may serve as the lowerelectrode in addition to its function as a conveying means. Suitablewheels or rollers 23 are provided to minimize friction in the movementof the conveyor, these rollers being arranged to travel along tracksshown at 24, so as to predetermine the-path of the conveyor, at leastthrough the chamber l1. Adjacent to the entrance end of the chamber |1the conveyor 2| passes around a pair of idler sprocket members 25mounted on a shaft 26, these sprocket members being shown as five-sidedmembers, so as to accommodate the particular type of conveyor employed.Somewhat similar sprocket members 21 are iixedly mounted adjacent to theexit end of the chamber I1 on a shaft 28, which also carries fixedthereto a suitable driving wheel 29 driven by a flexible belt orsprocket chain 30 from a driving'means here shown conventionally as amotor 3|. While I have shown a direct drive from a motor and contemplatea continuous movement of the conveyor through the drying chamber, I alsocontemplate that iii its broader aspects, the invention is applicable toapparatus wherein a conveying means is moved intermittently through adrying chamber having, for example, doors at' the entrance and exit endsof the chamber which may be closed during the dwell periods of theconveyor and opened, possibly automatically, only when the conveyor isto move along another step in its movement. Furthermore, while' I haveshown a direct drive from a motor 3| to the shaft 28, I also contemplatethat any speed varying means such as a conventional Reeves Drive may beinterposed in the drive between any suitable prime mover and the meanswhich are per se used for driving the conveyor.

At the entrance and exit ends of the drying chamber the yarn ports arepreferably constricted both vertically and laterally as shown, toprovide only enough space to permit the introduction and removal of yarnpackages, while minimizing any inflow of air currents such as mightinterfere with the operations taking place within the device, includingparticularly the maintenance around each yarn package of an atmospheresubstantially vapor of the liquid being evaporated therefrom as has beendescribed more in detail in connection with Figs. 1 and 2. As above setforth, I contemplate the possibility of an intermittently moved conveyorand the provision of doors as shown diagrammatically at 32 and 33 forthe entrance and exit ends respectively, which doors would normally beclosed during the periods when the conveyor is not moving yarn packagesinto or out of the drying chamber. In either case however, i. e. withopen ports or intermittently closing doors at the ports, the ports willensure the maintenance within the chamber of a pressure substantiallyequal to the pressure of the atmosphere outside the chamber.

v9 plant in which the device of my invention may be located.

While I have shown and described but a few embodiments of my inventionand set forthin detail certain methods to be performed in accordancetherewith, I contemplate that both the apparatus and method phases ofthis invention may be varied as will occur to those skilled in the artand within the scope of the appended claims, which are to be construedvalidly as broadly as the state of the art permits.

' What is claimed is: i

1. The method of evaporating a substantially aqueous liquid from a rayonyarn package, comprising the steps oi positioning and supporting saidyarn package between spaced electrodes in a substantially closedchamber, applying to said electrodes high frequency electric energy togencrate heat within said yarn package to maintain the vapor pressure ofsaid liquid of the package higher than the vapor pressure of theatmosphere surrounding the package and evaporate the liquid atsubstantially the boiling point thereof, and at least substantially asearly as said high frequency electric energy is applied to the packagesubjecting the package to, and thereafter maintaining in said chamber inat least the immediate neighborhood of and substantially surroundingsaid yarn package, an atmosphere of substantially aqueous vapor atsubstantially atmospheric pressure.

2. The method according to claim 1 with the additional step of supplyingaqueous vapor from an external source to the inside of said chambersurrounding said yarn package so as to maintain an envelope of suchvapor about said yarn package during the evaporation of the liquidtherefrom.

3. The method of evaporating water from a rayon yarn package atsubtsantially atmospheric pressure, comprising the steps of positioningand supporting the yarn package between spaced electrodes in asubstantially closed chamber, applying high frequency electric energy tosaid electrodes to generate heat within said yarn package to maintainthe vapor pressure of the water of the package higher than the vaporpressure of the atmosphere surrounding the package and evaporate waterfrom the package at substantially 212 F., and atleast as early as thehigh frequency energy of the electrodes is applied to the packagesubjecting the package to an atmosphere of substantially water vapor insaid chamber and thereafter maintaining said atmosphere at leastimmediately and substantially surrounding said yarn package during theevaporation of water therefrom.

4. The method of evaporating a substantially aqueous liquid from a rayonyarn package at substantially the boiling temperature of said liquid atatmospheric pressure, comprising the steps of positioning and supportingsaid yarn package between substantially plane, parallel, spacedelectrodes in a substantially closed chamber, applying high frequencyelectric energy to said electrodes to generate heat substantiallyuniformly within said yarn package to maintain the vapor pressure ofsaid liquid of the package higher than the vapor pressure of theatmosphere surrounding the package, and at least substantially as earlyas the package is subjected to saidelectric energy subjecting thepackage to an atmosphere consisting substantially of aqueous vapor andthereafter maintaining an atmosphere substantially of aqueous vapor atsubstantially atmospheric pressure in said chamber at least immediatelyand substantially surrounding said yarn package.

5. The method of continuously drying rayon yarn packages, comprising thesteps of substantially continuously passing such yarn packages along apredetermined path through a substantially closed chamber and at least apredetermined portion of which path in said chamber is between spacedelectrodes, maintaining a substantially uniform electric field on eachof the yarn packages during its passage along said portion of the path-by impressing high frequency electric energy onto said electrodes, andthereby maintaining the vapor pressure of the water of said packageshigher than the aqueous vapor pressure of the atmosphere surrounding thepackages and vaporizing water of the packages at substantially theboiling point thereof vat atmospheric pressure, and at leastsubstantially as early as each package is subjected to said fieldsubjecting the respective package to an atmosphere consisting ofsubstantially water vapor at substantially atmospheric pressure, andthereafter maintaining an atmosphere consisting substantially of watervapor at substantially atmospheric pressure in said chambersubstantially around each of said packages during at least its passagethrough the portion of its path that is within such electric eld. g

6. Apparatus for evaporating a, substantially aqueous liquid from arayon yarn package at substantially atmospheric pressure, comprising asubstantially closed chamber open to the atmosphere so as to insure themaintenance of substantially atmospheric pressure therein, a generatorfor generating high frequency electric energy, a pair of spacedelectrodes in said chamber receiving energy from said generator toestablish a substantially uniform electric field in the yarn package forheating said yarn package and the aqueous liquid therein substantiallyto the boiling point of such liquid at atmospheric pressure andmaintaining the vapor pressure of the aqueous liquid of a package higherthan the pressure of the aqueous vapor of the atmosphere within thechamber, means for maintaining said electrodes at a temperature at leastas high as that of the boiling point of said liquid at substantiallyatmospheric pressure, means for supporting .said package in said fieldin said chamber and means for maintaining in said chamber, independentlyof a. particular package being treated, an atmosphere substantiallyvapor of the liquid being evaporated in at least the immediateneighborhood of and substantially surrounding said package.

'7. Apparatus for evaporating Water from a yarn package at substantiallyatmospheric pressure, comprising a generator for generating highfrequency electric energy, a hollow lower electrode above which a yarnpackage is adapted to be supported, means for supplying low pressuresteam to the interior of said lower electrode to' maintain it at atemperature at least 212 F., a series of holes in the upper portion ofsaid lower electrode so positioned as to conduct steam from the interiorthereof to the region around said yarn package so as to establish andmaintain an atmosphere of steam surrounding the yarn package during thedrying thereof, an upper electrode located at substantially apredetermined distance above a yarn package positioned as assuma 11`aioresald. means for heating said upper electrode to maintain it at atemperature at least 212 F., and means for supplying highirequencyelectric energy from said generating means to said electrodes toestablish an electric iield therebetween.

8. Apparatus for evaporating water from a yarn package at substantiallyatmospheric pressure, comprising a generator for generating highfrequency electric energy, a hollow lower electrode serving as a.support for a yarn package, a hollow upper electrode substantiallyparallel with said lower electrode and spaced above a yarn packagesupported on said lower electrode by substantially a predetermineddistance, means for supplying low pressure steam to the hollow interiorportions of said electrodes, an annular series of holes in the upperwall of said lower electrode surrounding a yarn package thereon for theilow of steam from the interior of said lower electrode to the regionabout said yarn package and thereby for establishing and maintaining anatmosphere consisting substantially of steam in the vicinity of andsubstantially surrounding a yarn package on said lower electrode, andmeans for supplying high frequency electric energy from said generating'means to said electrodes to establish an electric eld therebetween.

ALFRED s. BROWN.

REFERENCES CITED The following references are of record in the ille ofthis patent:

` UNITED STATES PATENTS Number 698,059 Germany Oct. 3l, 1940

